The invention relates generally to a reluctance change sensor and more particularly to a reluctance-responsive digital tachometer for generating electrical pulses at a rate indicative of the speed of rotation of the rotating shaft.
In many mechanical systems utilizing rotating shafts, it is frequently necessary to accurately measure the number of revolutions per unit of time, hence the speed of rotation of the shaft. Many systems of the prior art have been designed to generate and count electrical pulses as a measure of the speed of shaft rotation. Common techniques utilize optical encoders associated with the shaft wherein an optical slotted disk is mounted on the shaft and provided with a ring of spaced slots on the outer periphery thereof. A light source and light detector are aligned on opposite sides of the disk such that a pulse of light is passed to the light detector as each of the slots passes between the light source and the light detector as the disk rotates with the shaft. Each pulse of light which is received by the light detector is processed and counted, the total count being proportional to the number of complete or partial rotations of the shaft.
Many of the systems of the prior art are subject to various errors; are operable only over relatively narrow ranges of shaft speeds; and are dependent upon the diameter of the slotted disk. Many such systems employ complex and relatively expensive circuitry for generating and counting the pulses, and errors often occur in the optical portion of such systems.
Some systems of the prior art have employed a toothed magnetic disk attached to a rotating shaft and employed a magnetic pickup which responded to the magnetic teeth of the disk for generating an analog signal as each tooth passed the magnetic pickup. Such systems have generally required rather sophisticated circuitry for shaping the resulting pulses or employed complex circuitry for detecting peaks of predetermined magnitudes or the like, and were operable over relatively narrow ranges of rotational shaft speeds. None of the magnetic systems of the prior art are accurate from extremely low shaft rotation speeds to extremely high shaft rotation speeds regardless of the sophistication of the circuitry involved, and none of the relatively simple circuits employed gave well-defined digital pulses over a reasonable range of speeds such as may be obtained with the circuit of the present invention.